Technical Abstract:
Substrate cost has been identified as the factor that affects butanol production economics the most. Hence, we identified a number of economically available substrates for this valuable fermentation. These substrates include corn stover (CS), wheat straw (WS), barley straw (BS), and switchgrass (SG). These residues and energy crops were pretreated using dilute sulfuric acid at 121 deg C for 1 h and hydrolyzed using enzymes [Celluclast 1.5 L (cellulase; supplier - Sigma Chemicals); Novozyme 188 (beta-glucosidase; supplier - Sigma Chemicals); and Viscostar 150 L (xylanase; supplier - Dyadic Corporation, Jupiter, FL, USA)]. The hydrolysis was completed in a 72 h period and resulted in sugar concentrations ranging from 40 to 65 g/L. The hydrolysates were then subjected to fermentation using Clostridium beijerinckii P260. In most cases, the culture was unable to grow and produce butanol due to the presence of fermentation inhibitors that inhibited both cell growth and fermentation. Hence, we developed processes where the hydrolysates were successfully fermented without any treatment to remove inhibitors. In the fermentation broth, 14.2 to 28 g/L acetone butanol (AB) were obtained. It should also be noted that use of such substrates requires hydrolysis, fermentation, and recovery to be performed in three separate units. To economize butanol production further, we were able to combine these three processes into a single "integrated process."